Exhaust Heat Driven Rankine Cycle for a Heavy Duty Diesel ... · Exhaust Heat Driven Rankine Cycle for a Heavy ... Hybrid e-motor or ... Waste heat source . Heat engines…. •Rankine

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Exhaust Heat Driven Rankine Cycle for a Heavy Duty Diesel Engine

October 5, 2011 Rakesh Aneja, Sandeep Singh, Kevin Sisken Detroit Diesel Corporation Roland Dold, Heijo Oelschlegel Daimler AG

Public Information

Public Information DTNA / DDC Super Truck Team 2

Waste Heat Recovery (WHR) Fuel Economy Targets • Improve fuel economy 5% on a commercial heavy duty truck • Improve engine brake thermal efficiency (BTE) by 3% points; contributing to

overall goal of 50% engine BTE

Aerodynamic Losses

Rolling Resistance

Drivetrain Losses

Auxiliary Loads

Radiator (incl. EGR), 22%

Exhaust, 22%

Charge Air Cooler, 8% Ambient and Residual,

5%

Auxillaries, 3%

Drivetrain, 3%

Aerodynamic, 18%

Rolling Resistance, 10%

Grade, 6%

Acceleration & Inertia, 3%

Waste Heat


WHR Relevance and Motivation • Daimler’s Super Truck project to demonstrate technologies for 50%

improvement in freight efficiency by 2015

• Daimler’s goal to continuously improve fuel efficiency of its production vehicles

• EPA/ NHTSA legislation to reduce GHG emissions and improve fuel efficiency of on-road heavy duty vehicles

• Nation’s energy independence


WHR Strategy – Heat Engine

Waste Heat Sources

Quality Quantity

Exhaust High High

EGR High Low

Coolant Low High

Intercooler Low Low

Hybrid e-motor or batteries

Ambient

Waste heat source

Heat engines…. • Rankine cycle • Brayton cycle • Stirling cycle • …

Heat engine pictorial source: Wikipedia


Exhaust Waste Heat Utilization – Rankine Cycle

generator

boiler

power expander

condenser

pump

turbo

EGR

ATD

compound


EGR Waste Heat Utilization

• High temperature, high quality

• Energy content contingent on matching of EGR, air and aftertreatment (ATS) systems

• Low EGR – high efficiency ATS • High EGR – low efficiency ATS

• Smaller engine radiator, bigger Rankine condenser

• Can boost fuel economy advantage of WHR, but increased complexity


Is EGR WHR Required? • EGR WHR increases design and control complexity

• Improvement in overall BTE

• Simulations have been performed

• Strong function of system efficiency and EGR flow rates

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

w/o EGR w/ EGR

WH

R F

E ga

in %

Validation Required!

generator

boiler

power

expander

condenser

pump

EGR

turbo

ATD

compound


Rankine Major Components

Evaporators Low pressure drop Avoid local hot-spots

Handle 2-phase flow Speed matched to generator Hermetically sealed

Expander

Condenser

Indirectly cooled (not working fluid to air) Matched to vehicle cooling capacity

Pump

Hermetically sealed

Working Fluid

Low environmental impact Thermodynamically suitable

for Rankine cycle


Expanders + Generators • Several expander technologies have been studied: screw, turbine, piston,

scroll, etc.

• Piston and scroll expanders are primary candidates

• Scroll expander

• High efficiency • Hermetically sealed • Handles two-phase flow

• Piston expander

• High pressure ratios

• Wound field synchronous generator (WFSG) for high voltage DC output to hybrid truck

• Magnetic coupling between generator and expander – simplifies sealing and design issues for generator


Working Fluid Selection

• Selection criteria …

• Low environmental impact • Thermodynamic performance • Saturation vapor curve with positive

slope • Acceptable operating pressures • High stability temperature • High vapor density • …

• Ethanol Selected


Condenser Cooling and Vehicle Impacts

• Significant under hood cooling burden

• A portion of exhaust heat recovered as work

• Majority tail-pipe exhaust heat rejected under hood

• Re-sizing and/ or addition of radiators, pumps, and fans required

• Engine coolant can be used for condenser cooling for certain working fluids and systems

• A low temperature cooling circuit is also being considered

Condenser Pressure

Eth

anol

Boi

ling

Poi

nt


Vehicle Cooling Strategies • Majority of former tail pile heat now rejected under hood

• Besides conventional ram air, alternate strategies can be considered

• Under chassis • Side of the frame • Back of the cab • Etc.

• Trade-offs due to weight, packaging, special ducting, fan on time, and aero complexities


Waste Heat Recovery Test Stand

WHR Boiler

Charge Air

Cooler

Engine

Engine Dyno

Pump Tank

Condenser Expander & Generator

Aftertreatment


E- Motor

Expander Generator

Condenser

Pump

Battery

Engine Transmission

Exhaust Aftertreatment

Boiler

Power Generation and Hybrid Integration


Vehicle Integration & Challenges

• Vehicle integration is a very significant challenge • Increased tractor weight (+350 lbs = -1% fuel economy) • Packaging space • Condenser cooling

• Cooling capacity will be challenged • Bypassing some waste heat is being considered

• Integration of electrical power generation with a hybrid vehicle • Controls implementation and interactions


Department of Energy Headquarters

• Gurpreet Singh • Roland Gravel

National Energy Technology Laboratory

• Carl Maronde This material is based upon work supported by the Department of Energy National

Energy Technology Lab under Award Numbers 409000-A-N8, DE-FC26-00-OR22805, and DE-EE-0003348.

Disclaimer: This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.

Acknowledgments

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Exhaust Heat Driven Rankine Cycle for a Heavy Duty Diesel ... · Exhaust Heat Driven Rankine Cycle for a Heavy ... Hybrid e-motor or ... Waste heat source . Heat engines…. •Rankine